1. Field of the Invention
The present invention relates to a bearing structure containing a gear shaft and so on, used for a focusing mechanism of a camera, for example.
2. Description of the Related Art
Conventionally, a gear mechanism provided in a focusing mechanism has a gear shaft, made of plastic material, and a bearing member having a U-shaped groove to support the gear shaft. The gear shaft has a pair of flanges and a small diameter portion formed between the flanges. The small diameter portion is rotatably supported by the groove, and the flanges are in slidable contact with the end surfaces of the bearing member. Thus, the gear shaft is rotated about the axis thereof, while axial movement of the gear shaft is prevented by the flanges.
The gear shaft is manufactured using molds, and thus, a parting line is formed on a surface of the gear shaft, because of a dividing portion of the molds. The parting line extends in the axial direction of the gear shaft, along the surfaces of the flanges and the small diameter portion, and a flash or an unwanted projection may remain on the parting line. The flash interferes with the groove or the end surfaces, and may prevent the gear shaft from rotating smoothly. Thus, the flash may be removed during the manufacturing process so as to ensure the smooth rotation of the gear shaft. However, the removing process increases the cost of the gear shaft, and is troublesome.
Instead of removing the flash, a plane may be formed beforehand on a portion of the gear shaft, through which the parting line passes. The depth of the plane must be greater than the size of a flash which might occur, so that the flash is prevented from coming into contact with the groove or the end surfaces. However, because of the recess, a step is formed on the gear shaft, and this step may interfere with an edge between the groove and the end surface, so that the problem regarding the smooth rotation may not be fully resolved.
Therefore, an object of the present invention is to provide a bearing structure, which enables a smooth rotation of a gear shaft, and which is simple and obtained without increasing the cost.
According to the present invention, there is provided a bearing structure comprising a rotational shaft and a bearing member.
The rotational shaft has a pair of flanges located at axially different positions, and a small diameter portion provided between the pair of flanges. The small diameter portion has a diameter smaller than diameters of the flanges. The flanges have end surfaces facing each other, on which first tapered surfaces are formed. The first tapered surfaces taper down to the diameter of the small diameter portion as the first tapered surfaces approach the small diameter portion. The bearing member has a pair of restraining surfaces, a support groove formed between the pair of restraining surfaces to support the small diameter portion, and second tapered surfaces formed between the support groove and the restraining surfaces. The small diameter portion is fit in the support groove while the first tapered surfaces are engaged with the second tapered surfaces. A flank is formed on at least one part of the flanges that face each other and at substantially the same circumferential position on those flanges, to form a gap with one of the second tapered surfaces.